Taiwan Patent No. 181907 discloses an improved catalyst for use in a partial oxidation of methanol to convert methanol into formaldehyde. Said catalyst includes a molybdenum oxide active catalytic material and an ingredient M, wherein M is selected from the group consisting of Cr, V, Al, W, Mn and a mixture thereof, and the molar ratio of Mo: M is of 1-5. Another improvement of this prior art invention includes using a lithic-structured inert material as a carrier of the catalyst. Said carrier is composed of SiO2-rich fiber, which has an average diameter of 50 to 250 microns and a length of 2 to 30 mm. Said catalytically active material on the carrier comprises 1-90%, preferably 80-90%, of the total amount of the active material and lithic carrier.
Taiwan Patent No. 531544 discloses a process for preparing formaldehyde through a dehydrogenation reaction of methanol, which comprises performing the reaction under conditions where a carrier gas at a temperature of 300 to 1000° C. is introduced into a reactor and in the presence of a catalyst, characterized in that the temperature of the carrier gas stream entering the reactor is higher than the dehydrogenation reaction temperature for at least 20° C.
Taiwan Patent Publication No. 200624167 discloses a process for oxidizing hydrocarbons, alcohols, or aldehydes, which comprises oxidizing hydrocarbons, alcohols or aldehydes into corresponding alcohols, aldehydes, carboxylic acids or carboxylic acid esters in a liquid phase consisting of a region containing oxygen and a region substantially free of oxygen in the presence of a Pd-containing catalyst, wherein said region substantially free of oxygen comprises 0.1 to 10 vol % of the sum of said region substantially free of oxygen and said region containing oxygen.
Taiwan Patent Publication No. 200631656 discloses a process for preparing a catalyst for oxidizing methanol into formaldehyde, which comprises reacting iron powder with MoO2 in an aqueous suspension solution at a Mo/Fe ratio of 1.5 to 5 and at a temperature of 20 to 100°, and subsequently, as required, using an oxidation agent to oxidize said mixture, wherein the amount of oxidation agent is equal to or greater than an amount required to oxidize ferrous ions into ferric ions and to oxidize Mo+4 to Mo+6 state.
Taiwan Patent Publication No. 200643004 discloses a process for preparing a concentrated formaldehyde aqueous solution, wherein methanol receives an oxidation dehydrogenation reaction at 590-690° C. in the presence of a silver catalyst to produce a 59 wt % concentrated formaldehyde aqueous solution. According to this prior art invention, the reaction medium carries away a huge amount of reaction heat, thereby promoting the oxidation reaction and achieving the objectives of high concentration of formaldehyde and low concentration of residual methanol.
Most of the conventional catalysts are prepared by depositing metal on a carrier by immersion or co-precipitation. The conventional catalysts so prepared are inevitably suffering from the defects of metal sintering under a high temperature thermal treatment environment or high temperature reaction condition, causing a great reduction in surface area of the catalyst metal, so that problems such as aging, decreasing in reaction activity or decreasing in product selectivity occur. Therefore, a new catalyst is required to replace an aged catalyst after a period of operation.
The inventors of the present application disclose a novel catalyst having a core-porous shell structure and a process for preparing the same [Microporous and Mesoporous Materials 98 (2007) 208-213 (published on the internet in October 2006)]. This novel catalyst is composed of silver nano particles and a porous SiO2 shell material encapsulating the silver nano particles. Furthermore, the core-porous shell structure of this novel catalyst remains un-damaged at 1000° C. Thus, such a catalyst has the potential of being used as a catalyst for high temperature reactions. The disclosure of this article is incorporated herein by reference.